User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.4577.82 Safari/537.36

Steps to reproduce:

Update TB to 91.1.1.
Have US (English) version of TB, where folder names are "Inbox", "Sent".
For IMAP accounts I have Polish name "Wysłane", which is renamed "WysBane" in virtualFolders.dat.
Even adding the Wysłane (Sent) folder to Sent unified folder does not help to see messages from that IMAP accounts (which are surely sent, and they are visible in single folder for that account).

Actual results:

In effect, for two IMAP Inbox (Odebrane) folders the emails are visible in messages list, but are not visible for Sent (Wysłane/WysBane).
Seems like there is some problem with encoding for virtualFolders.dat or any operation earlier/later.

Expected results:

All selected accounts messages should be visible in unified folder Sent.